ALKALINE MAGMATISM AND THE EVOLUTION OF T HE OXIDATION POTENTIAL OF THE EARTHS MANTLE

The earth's atmosphere and, subsequently, mantle underwent oxidation a t the Archean-Proterozoic boundary (2.5-2.7 Ga) due to a change in the planet's geodynamic regime. This oxidation gave rise to a global meta somatic mass transfer and produced trace element-enriched zones in the subcrustal region-a source of alkaline magmatism. The synchroneity of these events (atmospheric oxidation and the appearance of alkaline ro cks) cannot be a mere coincidence and doubtlessly indicates that these processes were closely related.